Match List I with List II
| List I | List II |
| A. Impurity defect | I. \(NaCl\) with anionic sites called F centres |
| B. Metal excess defect | II. \(FeO\) with \(Fe^{3+}\) |
| C. Metal deficiency defect | III. Non ionic solids and density of solid decreases |
| D. Simple vacancy defect | IV. \(NaCl\) with \(Sr^{2+}\) and cationic sites vacant |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-IV, B-I, C-II, D-III
Point defects are either stoichiometric (vacancy, interstitial, Schottky, Frenkel), impurity defects, or non-stoichiometric (metal excess, metal deficiency).
(A) Impurity defect — This matches (IV) NaCl with Sr2+ and cationic sites vacant. When NaCl crystallises with a little \( \ce{SrCl2} \), each \( \ce{Sr^2+} \) takes the place of two \( \ce{Na+} \) ions: it occupies one site and leaves the other cationic site vacant.
(B) Metal excess defect — This matches (I) NaCl with anionic sites called F centres. NaCl heated in sodium vapour gains \( \ce{Na+} \) on the surface; the released electrons occupy anionic sites, called F-centres, which make the crystal yellow.
(C) Metal deficiency defect — This matches (II) FeO with Fe3+. In FeO (about Fe0.95O) some \( \ce{Fe^2+} \) ions are missing, and the lost positive charge is made up by \( \ce{Fe^3+} \) ions.
(D) Simple vacancy defect — This matches (III) Non ionic solids and density of solid decreases. Some lattice sites are empty, so the density falls; this defect is shown by non-ionic solids.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.